A flow sensor with metal film resistor is provided for an electrically controlled fuel injection system of an internal combustion engine of an automobile and the like and is used for an air flow meter that measures the intake air flow. Presently, the thermal type air flow sensor with metal film resistor goes mainstream because it can directly detect the mass air volume.
In particular, constant attention has been focused on a thermal airflow sensor fabricated by the semiconductor micro-machining technology because such sensor can reduce costs and operate on low electric power. For example, JP-A No. 213470/1998 discloses a conventional airflow sensor technology. The technology uses platinum (Pt) for a heater element (heater) and a temperature detection element (sensor). The technology discloses a diaphragm structure fabricated by removing Si films from the bottoms parts of the heater and the sensor. The method disclosed in JP-A No. 287687/1999 uses a heater element (heater) and two temperature detection elements (sensors) sandwiching the heater at the sensor center. The heater and the sensors are fabricated by, forming a groove in an oxidized film, embedding a platinum film, and flattening the film through the use of chemical mechanical polishing (CMP).